In recent years the field of medicine has witnessed the application of lasers for therapeutic treatment of a variety of diseases and conditions. Laser energy conducted through a flexible waveguide such as an optical fiber has been used successfully for hemostasis, photodynamic destruction of some forms of tumors, removal of epidermal growths and abnormalities, and the like.
Lasers have also been adapted for use in surgical procedures, and surgical devices have been built, tested, and sold commercially. However, some drawbacks in laser devices for surgical use have been noted in the prior art. For example, U.S. Pat. Nos. 4,693,244 and 4,736,743 discuss the use of a bare optical fiber connected to a laser and used to cut tissue. It is noted that if the bare fiber end contacts the tissue being cut, the fiber becomes fouled, the transmission efficiency decreases, more heat is generated in the fiber, thermal runaway ensues, and the fiber quickly heats to the point of material failure. One attempted solution to this problem in the prior art is to use the fiber end in a non-contact mode, thereby avoiding contamination of the fiber output end. However, contamination is difficult to avoid in practice, due to the fact that the fiber must be held very close to the tissue target, and tissue contact is unavoidable. A single contact with tissue will often result in fiber failure. Also, the smoke and vapor arising from the laser beam impact site can contaminate the fiber end without any contact with the tissue itself.
Another attempt to solve this problem has been the provision of a transparent tip secured to the output end of the optical fiber, the tip being formed of a material such as sapphire that is tolerant of extremely high temperatures. If the tip becomes fouled or coated with carbonized material, it will not be heated to the point of material failure. Several manufacturers make available surgical optical tips having differing cutting configurations. However, even sapphire can be fractured by the high temperatures and temperature transitions experienced at the optical fiber output end. Moreover, sapphire or any similar material is expensive and difficult to manufacture, and the surgical tips can be reused only a few times.
A surgical tip, as well as a bare optical fiber end, may be subject to a constant flow of gas or liquid to cool the heated end and to remove some of the inevitable contamination. In some procedures, gas cooling can create the risk of embolism in the patient, and liquid cooling can cause such problems as fluid distension, fluid absorption through the surgical wound, and the like.
The simplest practical solution available in state of the art surgical lasers is to limit the laser power to a level that cannot damage the optical fiber. Ironically, this approach requires that a laser capable of delivering high power; e.g., 120 watts of beam energy, must often be limited to 30 or 40 watts output to preserve the optical fiber integrity. Alternatively, the optical fiber output end must be constantly immersed in a laser-transparent liquid, such as water, during operation, or the tip must remain in contact with the tissue during operation so that the tissue cools the fiber tip. This conditions are difficult to achieve in practice.